Although Silicone polymers have very low mechanical strength, it is effective to add silica thereto in order to improve the reinforcement. Many silicone rubber compositions therefore include silica. However, the silicone polymer and silica charge negatively due to friction, thus the mixture shows highly negatively-charged friction potential. From this reason, when obtaining the silicone rubber compound including silica, the compound is highly negatively charged in the course of mixing, and accidents such as ignition and explosion may possibly be caused by this electric potential. In particular, the blending of a dangerous substance such as a silane compound or hexamethyldisilazane causes a greater danger, and therefore usually the production is performed in a sealed mixer under an atmosphere substituted by nitrogen as a main way for avoiding the danger. However, it cannot be said that the safety is completely secured, in consideration of accidental errors such as human mistakes or malfunctions of measuring instruments; for example, the nitrogen substitution is not sufficiently completed due to some troubles, or even if the nitrogen substitution is completed, a small orifice is opened for adding additives.
In order to blend the silicone rubber composition including silica with a vulcanizing agent or a coloring agent in processing manufacturers, there exists generally a step of mixing them together by using rolls or in a mixer. In this case, due to negative friction charge generated during the mixing time, dust easily adsorbs and troubles in which the dust contaminates the product as foreign substances are often observed. In particular, most of silicone rubbers are molded products having a semi-transparent appearance and therefore, the inclusion of even a slight amount of the foreign substances would cause problems.
On the other hand, JP-A 2002-363294 proposes a method of addition of a cationic antistatic agent or deionized water, against the friction potential charged, in order to greatly increase an amount of filler. According to the method, however, many of the cationic antistatic agents do not have high heat resistance and thus lose their effects in several hours in a heating process at temperatures of, for example, 150° C. to 200° C. Further, at least about 1000 ppm of the blending amount thereof is required, which may possibly exert adverse effects on the properties or appearance of the rubber. Similarly, the deionized water or city water also evaporates due to heat generated during the mixing time, whereby stable effects cannot be expected, and moreover, if the water is blended with silica, silica disadvantageously agglomerates to form foreign substances.
As described above, according to the method described in JP-A 2002-363294, the problems to be solved by the present invention cannot be solved.
In addition, JP-A 2005-298661, JP-A 2005-344102, JP-A 2006-83211, JP-A 2006-225422, and JP-A 2006-265340 propose a blending of an ion-conductive compound such as a specific lithium salt and the silicone polymer, but any of them are different from the present invention in terms of a composition or curing mechanism as well as an amount of the ion conductive compound to be added and the intended object, and accordingly the problems to be solved by the invention cannot be also solved by these methods.